Strange behavior with iCalendar invites.

Zimbra 5.0.18.

I have a hand full of reports from users describing some odd behaviour with appointment invites sent to them from other users, using Apple's iCalendar.

They report that they receive more than one invite, and that they appear outright broken. One report is that the invite came in, and the body was empty, but it still allowed the recipient to accept the invite. In that case, they also received two more copies, neither of which allowed them to accept the invite. One of them had the body of the message in it,

Most of the time, these invites work without a problem. Just these few reports havent.